Resilient seals, for the purpose of confining fluids at high or low temperatures and/or pressures, are known and used in numerous applications, such as applications where a fluid (liquid and/or gas) is to be confined between cooperating components, the sealing faces of which are varying distances from one another.
Resilient metallic seals produced from materials having desirable high temperature, fatigue, relaxation, and oxidation resistant properties are useful for their ability to accommodate variations in operating length (the distance between sealing surfaces in cooperating members of a joint) in the direction of the longitudinal axis of the seal (the axis perpendicular to the circumference of the seal). Variations in operating length may, for example, occur due to one or a combination of the following: relative thermal expansions or contractions of components and assemblies in which a seal is housed; mechanical vibration; sealing face deformations; or varying separation of adjacent sealing face surfaces as a result of initial assembly or subsequent re-assembly after maintenance or repair. Of course, it will be recognized that the preceding list is not exclusive and represents examples of various modalities by which variations in operating length may occur. It is desirable that a seal remain in constant contact with each sealing surface so as to prevent leakage of fluid into or out of a system, depending on the placement of the seal and the area of high pressure in relation to the seal.
Some resilient seals rely upon internal spring forces and pressure energization to establish and maintain contact forces sufficient to ensure low leakage rates. Convolution type seals, such as multiple-convolution seals or single-convolution seals, such as for example those with general E-shaped cross-section, are particularly well suited for applications which require the accommodation of sealing face displacement along the longitudinal axis. Such seals, for example, may be used where high temperatures and ease of disassembly of joints is vital to the economic operation of systems, such as in applications associated with aircraft engines. Examples of convolution seals are disclosed in U.S. Pat. Nos. 3,797,836 and 4,121,843, both to Halling.
For applications in which axial deflections are extreme, multiple-ply seals, such as those in accordance with U.S. Pat. No. 5,249,814 to Halling, may be employed. An advantage of multiple-ply seals is that they can accommodate n times the amount of axial displacement as a single-ply seal, while containing the same level of pressure or vacuum. The variable "n" represents the number of plies of the seal.
However, in some seals of the prior art, an example of which is shown in FIG. 1, a limitation for displacement along the longitudinal axis L may be reached when a bending stress in a crest 2 or a root 4 of a seal 1 approaches a limiting value of, e.g., yield stress, fatigue stress, or relaxation stress, of the material from which the seal is constructed.